The long term goal of the work continues to be an attempt to understand more fully the signals and interactions that occur between the uterine epithelium and the conceptus. In the coming year 1) we shall attempt to purify and to characterize more completely an inhibitor of plasminogen activator that is produced by the pig endometrium under the influence of progesterone. We believe that this inhibitor might be involved in protection of the uterine surface from proteases released from the conceptus and may prevent invasive growth; 2) we plan to purify the major secretory product of the cow and pig blastocysts and attempt to evaluate their function; 3) studies will continue on conceptus steroid metabolism; 4) antibody will be raised against the major polypeptide secreted by the sheep blastocyst in order to determine its site of synthesis and mode of interaction with maternal tissue; 5) Use culture conditions which resemble the hormonal status of the estrous cycle of pigs and attempt to induce cyclical changes in cultured endometrium; 6) purify placental lactogen from the cow and sheep and, 7) investigate further the conditions which promote release of secretory product from the endometrium of the pig.